Data storage is an important function of the computer systems that are employed by businesses, universities, individual computer users, etc. Data storage systems enable the storage of vast amounts of information that can be used in a variety of ways. Computer data storage involves the use of magnetic and/or optical devices to store information. A component of many computer data storage systems is a disk drive. A disk drive is an assembly that is designed to store and retrieve information through the use of spinning magnetic media and an actuating magnetic transducer (read/write head).
A read/write head is the electromagnetic component in a disk drive (or tape drive) that reads and records data on a magnetic surface. Read/write heads can employ read-back signals, which carry data that is read from a disk, that have either longitudinal or perpendicular orientations. The use of read/write heads that are employed in perpendicular recording has increased as recording technology has developed. Read-back signals routinely exhibit noise in the form of various types of non-linear distortions that can detrimentally affect the performance and storage capacity of a recording device. Non-linear distortion types may include over write (OW), MR asymmetry (MR ASYM), and non-linear transition shift (NLTS), and others.
The capacity to accurately characterize non-linear distortions that are exhibited by the read-back signals of a read/write head of a recording device is critical to effective analysis of their performance. The accurate characterization of non-linear distortion enables the elimination or diminution of the distortion that is exhibited by the signals through the use of basic signal processing techniques.
Conventional systems that are used to characterize non-linear distortions are designed to characterize the non-linear distortions that are exhibited by longitudinal signals. It should be appreciated that longitudinal signals contain no direct current (DC) components. However, perpendicular signals that are increasingly being employed in read/write heads do contain DC components. Because many conventional non-linear distortion characterization systems are not designed to manage signals that contain DC components, these conventional systems are ineffective for characterizing the non-linear distortions of perpendicular signals. There typically exists high-pass filter in signal read-back path to the input of a read channel. The high-pass filter (AC coupling) eliminates DC components in read-back signal causing base-line of read-back signal to shift. The conventional non-linear distortion characterization systems become ineffective when read-back signals have base-line shift. Further, effective characterization of these non-linear distortions is crucial in reducing their signal contributions for accurate data recovery processing of the perpendicular read-back signal.